Pipe for transporting automobile fluids, comprising a smooth inner tube and an outer annellated tube

ABSTRACT

A pipe for transporting automobile fluids includes a smooth inner tube ( 1 ) based on an elastomer thermoplastic material, an outer annellated tube ( 2 ) in contact with the inner tube by the inner vertex of the undulations thereof and which is made of a polyamide-based thermoplastic material, in addition to an element connecting the outer tube to the inner tube.

The present invention relates to a pipe for transporting automobilefluids such as cooling liquid, fuel, windshield wiper fluid, . . . .

BACKGROUND OF THE INVENTION

Amongst the pipes used in a motor vehicle, there are smooth pipes oflarge diameter presenting bends and which are intended, for example, toform the fuel tank filler pipe. Such pipes are made by blow-molding.Unfortunately, that method of manufacture is relatively expensive.Attempts have been made to make such pipes by extrusion followed byhot-forming, since that method of manufacture is less expensive and alsomakes it possible to obtain pipes that are lighter than those obtainedby blow-molding. However, that method has been found to be difficultbecause extruded pipes tend to flatten while they are being shaped.

That type of problem is to be found in general manner in all smoothpipes made of plastics material that are shaped in such a manner as tohave bends so that their shape matches the environment in which they areto be installed. More particularly, such structures are not suitable fordiameters in excess of 25 millimeters (mm) since they are difficult toshape by thermoforming: a smooth pipe of large diameter tends to kink assoon as too small a radius of curvature is imparted thereto.

Attempts have been made to replace such smooth pipes with corrugatedpipes which are easier to shape. Nevertheless, such pipes lead toproblems of fluids foaming, in particular of fuel foaming, problems ofnoise, and problems of head loss.

Furthermore, another drawback of the pipes presently in use lies in thefact that it is difficult to obtain permeability to automobile fluidsthat is low enough to enable them to perform their function effectively.This drawback is particularly harmful in corrugated pipes which presenta large surface area in contact with the fluid.

To obviate that drawback, is it known to use multilayer pipes, but theytoo are relatively expensive.

OBJECT OF THE INVENTION

It would thus be most advantageous to have automobile fluid transportpipes that remedy the drawbacks of prior art pipes, at least in part.

BRIEF DESCRIPTION OF THE INVENTION

To this end, the invention provides a pipe for transporting automobilefluids, comprising a smooth inner tube based on a thermoplasticelastomer material, a corrugated outer tube which is in contact with theinner tube via the inside peaks of its corrugations and which is made ofa thermoplastic material based on polyamide, and means for connectingtogether the outer tube and the inner tube.

The pipe obtained in this way is particularly well adapted totransporting automobile fluids and presents good aptitude to beingshaped, in particular by being deformed elastically. The pipe is alsosimple and inexpensive to make. The thermoplastic elastomer materialused for the inner tube also makes it simple to provide strongconnections with the members to which the pipe is connected, e.g. bymeans of nipples secured to members and forced into the inner tube.

In a particular embodiment, the tubes are single-layer tubes, thepolyamide used is a polyamide 12 and the thermoplastic elastomer is amixture of polypropylene and an elastomer based on ethylene propylenediene monomer (EPDM).

This embodiment presents very good characteristics for transportingautomobile fluids.

Other characteristics and advantages of the invention will appear onreading the following description of a particular and non-limitingembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

Reference is made to the sole accompanying figure which is a fragmentaryhalf-view in longitudinal section of a pipe in accordance with theinvention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

With reference to the figure, the pipe of the invention comprises aninner tube given overall reference 1, and an outer tube given overallreference 2, surrounding the inner tube 1.

The inner tube 1 is a smooth tube, in this case being of single-layerstructure and made of a thermoplastic elastomer material. Thethermoplastic elastomer material used is a mixture of polypropylene andof a rubber based on EPDM, such as one of those produced under thereference Santoprene by the supplier Advanced Elastomer Systems.

The outer tube 2 is a corrugated tube in which the corrugations haveinside peaks 3 of inside diameter equal to or substantially very closeto the outside diameter of the inner tube. The tubes 1 and 2 areconnected together either at each of the inside peaks 3 by adhesive orby bonding, e.g. during a coextrusion method, or else, if the pipe is ofdetermined length, merely at its ends by putting the outer tubemechanically into abutment against a flange on the inner tube 1 with orwithout adhesive between the ends of the tubes 1 and 2. When it isdesired that the inner and outer tubes 1 and 2 be secured to each otherat each inside peak 3 of a corrugation in the outer tube 2, thematerials selected are naturally suitable for bonding together or forbeing stuck together.

The outer tube 2 in this case is of single-layer structure being made ofpolyamide, and preferably of polyamide 12.

The materials used may be recycled materials obtained, for example, bygrinding tube scrap, thereby leading to less pollution and achievingeconomic savings.

The tube is obtained by means of a conventional machine comprising anextruder head having a first channel for producing a “parison” or blankwhich, under the effect of external suction, is pressed against hingedmolds surrounding the extrusion head and moving parallel to the axisthereof. A second extrusion channel, downstream from the extrusion ofthe parison, enables the corrugated tube formed by the parison insidethe mold to be lined with a smooth inner tube, thus producing the pipeof the invention. Advantageously, a channel can be provided in theextrusion head between the corrugated tube and the smooth tube fordelivering an inert gas which will contribute to reducing thepermeability of the pipe of the invention. This inert gas which may beair, nitrogen, or any other suitable gas, can be maintained underpressure inside the corrugations of the corrugated tube, with thispressure constituting an isolating element combating migration of vaporfrom the inside or the outside through the walls of the tubes.

The connection between the two tubes is made in leaktight manner, andpreferably at each inside peak of a corrugation in the corrugated tube.

Naturally, the invention is not limited to the embodiment described andvariants can be applied thereto without going beyond the ambit of theinvention as defined by the claims.

In particular, a different thermoplastic elastomer material can be usedfor the inner tube. Furthermore, the inner tube may include an innerlayer that is conductive in order to evacuate the electrostatic chargethat is generated by friction of the transported fluid rubbing along thepipe. This limits any risk of explosion when the transported fluid isflammable. The material of the tube 1 is selected as a function of itschemical resistance to the fluid being conveyed, and also itspermeability relative thereto, whereas the material of the tube 2 isselected mainly for its characteristics of its resistance to the outsideatmosphere, its chemical inertness, its corrosion resistance and itsmechanical strength.

1. A pipe for transporting automobile fluids, the pipe comprising asmooth inner tube (1) based on a thermoplastic elastomer material, acorrugated outer tube (2) which is in contact with the inner tube viathe inside peaks (3) of its corrugations and which is made of athermoplastic material based on polyamide, and means for connectingtogether the outer tube and the inner tube.
 2. A pipe according to claim1, wherein the polyamide used is a polyamide
 12. 3. A pipe according toclaim 1, wherein the thermoplastic elastomer is a mixture ofpolypropylene and an elastomer based on an ethylene propylene dienemonomer.
 4. A pipe according to claim 1, wherein the inner tube (1) is asingle-layer tube.
 5. A pipe according to claim 1, wherein the outertube (2) is a single-layer tube.
 6. A pipe according to claim 2, whereinthe thermoplastic elastomer is a mixture of polypropylene and anelastomer based on an ethylene propylene diene monomer.
 7. A pipeaccording to claim 2, wherein the inner tube (1) is a single-layer tube.8. A pipe according to claim 3, wherein the inner tube (1) is asingle-layer tube.
 9. A pipe according to claim 2, wherein the outertube (2) is a single-layer tube.
 10. A pipe according to claim 3,wherein the outer tube. (2) is a single-layer tube.
 11. A pipe accordingto claim 4, wherein the outer tube (2) is a single-layer tube.